She'd spent more than 15 years in the corporate world, originally with Armourguard and then Forestry Corporation, which morphed into Fletcher Challenge Forests, working in roles that combined accounting with systems management.
After being made redundant from Fletcher while on maternity leave with daughter number three, she began helping out at Deacon Holdings.
"Then when [Grant's] accountant left two days before Christmas and I was about seven months pregnant, he asked me to come in and fill in for him for a while."
That was 8 years ago and since then her focus has moved from the accounting side to solving problems within the business.
"I just like to understand how things fit together. I'm a fairly logical person; I like to think I am. I like to be learning all the time, I like to find new things so for me accounting is such a small part of my job now."
Porteous is one of a team of four, including her husband, who provide mentoring for the 27 franchisees throughout the country. She looks after those who either gravitate to her straight-shooting style or need help managing their financial systems.
"I enjoy actually working with franchisees in their businesses and actually helping them. Sometimes it's easy on the outside looking in to just throw up possibilities," she says. "I don't think business is actually that complicated. People tend to make it really complicated."
A franchisee who was struggling five years ago, for example, was told to sell another business that was becoming a distraction, sell his own home to pay creditors, tidy up his premises and lift his professional standards. "And within about 18 months he actually became one of our best businesses."
She admits her approach is direct and to the point, whether it's providing feedback or making staff redundant.
"It becomes black and white with me. It's a business decision, it's not personal, and it is just a business decision. It needs to be done so you just do it."
The building business has had a tough few years and Porteous says their goal through the global financial crisis was for franchisees to survive.
"We actually came through relatively unscathed.
"We had one or two terminations in that time," says Porteous, but adds: "If they had done things differently they could have actually still had good profitable businesses."
Porteous says the firm is just beginning to rebuild homes in Christchurch but won't chase more work than it can handle without compromising quality.
"We think it's actually important with what Christchurch has been through. [For] a lot of the people it's not their choice to build and it can be a fairly stressful process so we actually want to do it well first time."
With economic optimism lifting, the goal is now to have all franchises building at full capacity again.
On the personal front, Porteous says she needs the challenge and mental stimulation of working, and would like to provide a good example for her four daughters.
"My children, they don't know any different. For them, women work and that's great."
